The object of the invention is a frame structure according to the preamble of claim 1. The invention relates to frame structures, particularly to mobile stations and other small-sized portable equipment operating at high frequencies.
Mobile phones utilize frame structures, to which the printed circuit board of the phone is fixed, whereby the frame structure is generally manufactured by casting, typically die casting, by deep drawing, by bending a metal sheet, or from metal coated plastic. Usually the frame structure comprises partitions which separate the components or component groups mounted on the device""s printed circuit board from each other, whereby the partitions also form an RF shield in order to reduce the power of the radio frequency radiation received or emitted by said component or component group. Typically the partitions also make the frame more rigid.
The purpose of the frame structure is typically to protect the internal components of the device and in addition to support the printed circuit board or boards and other components of the device, as well as to reduce any interfering radiation generated by device from spreading into the environment. A purpose of the frame is also to protect the device""s components from external electromechanical interference sources or signals being coupled to the components.
Previously there are many known ways to fasten components, such as printed circuit boards or corresponding, to the frame structure. Threadings can be made in the frame structure, particularly it its partitions or in pins made separately in the frame structure, so that the fastening can be made with screws. As the frame structures are often made very thin in order to minimize the weight of the device the partitions must often be equipped with bulges around the threadings so that there will be sufficiently material around the threads in order to achieve a firm fastening. One such solution is presented in the application publication EP-391 020, which presents a mobile phone frame structure. In the solution presented by the publication partitions are formed in connection with the frame structure so that the partitions have thickened places in partition corners and ends which enable fastening with screw. In a solution of this kind the components are fixed to the frame with the aid of screws, which complicates the manufacture of the frame structure and the assembly of the equipment. First the frame must be cast, after which the required threadings must be formed in different places of the structure. In the assembly phase the printed circuit board must be positioned accurately, so that the fastening holes in the printed circuit board are accurately registered with the threadings, and then the screws must be individually screwed. All this will result in a large number of work steps, which causes substantial costs in mass production.
The use of screws to fasten printed circuit boards and other components means that their corresponding threads require extra space in the frame structure and a corresponding space also on the printed circuit board which shall be fastened at that place, so that a component fastened on the printed circuit board will not be clamped between the printed circuit board and the fixing point. Thus a screw fastening consumes a substantial area on the printed circuit board.
In the mass production of mobile stations and corresponding devices it is essential that there is a minimum number of work steps and that they can be performed as fast as possible. Further, a maximally efficient use of the printed circuit board area is of primary importance in small-sized devices. Such devices must also be as light as possible, whereby it is an object to manufacture the components of the device of materials which are as thin and light as possible, but in spite of this the resulting device must be as rigid as possible and withstand blows, wear and torsion. Frame structures have been made for instance of plastics, on the surface of which a thin metal film is formed in order to obtain electrical protection characteristics. Plastic is a light material, but a problem is the low rigidity of plastic structures. In such cases the rigidity can be increased with the aid of partitions, but then the size of the device must be increased due to the space required by such extra reinforcing structures.
Magnesium has also been used as material for frame structures. Advantages of the magnesium is its lightness, the rigidity of structures made of it, and a possibility to realize versatile forms. Disadvantages of the magnesium are on the other hand a low resistance against corrosion and the high costs, and the threading bores also cause strength problems. Further a frame made of magnesium must be coated, which causes an extra work step. The coating also impairs the electrical characteristics of the magnesium frame, because the coating causes losses.
The object of the present invention is to eliminate the above mentioned disadvantages. An object of the invention is also a simple, cheap and durable structure. A further object of the invention is to realize a frame structure which is suitable to be used in mobile stations and other corresponding devices utilizing high frequencies, in which the frames must have a robust and rigid structure which acts as an efficient barrier against electromagnetic radiation and to which the device""s components can be fixed in a simple, easy and reliable manner.
The objects of the invention are attained by forming the frame structure by extrusion, and by forming the fixing means required for fastening the components during the extrusion. Such fixing means are preferably pin-like projections, which can be compressed into a rivet fixing the component. Such fixing means can also be strip-like clamping edges which are bent over the edges of the component. With the aid of fixing means of this type it is at the same time possible to form both a mechanical fixing and a good electrical contact between the component and the frame structure. During the extrusion it is also possible to fix parts made of other materials to the frame structure, such as fixing means of different types and other components, such as antennas.
The frame structure according to the invention is characterized in what is said in the characterizing clause of the independent claim concerning the frame structure. The invention also relates to a device, which is characterized in what is said in the characterizing clause of the independent claim concerning the device. Further the invention relates to a method, which is characterized in what is said in the characterizing clause of the independent claim concerning the method. The dependent claims represent other preferred embodiments of the invention.
According to a preferred embodiment of the invention a rivet fixing can act as the fixing mechanism which replaces the screw fastening. Then the rivets are extruded in connection with the partitions belonging to the structure, whereby the rivets are made as projections directed upwards from the partitions and having a thickness, which can be the same as that of the partition. In connection with the fixing of the printed circuit board the free area of the compartments separated by the partitions is not reduced due to the fixing means, and the area of the printed circuit board can be utilized more effectively for components, compared to the conventional use of screws. A separate work step to enable the fixing, for instance threading, is avoided because the fixing means are formed already during the extrusion. The use of rivets integrated in the frame also facilitates the assembly phase, because there is no need to mount separate fastening means. Compressing a rivet is also a rapid step compared to the turning of a screw. One of the means formed during the extrusion can also be left so short that it is not thicker than the printed circuit board, whereby this means acts only as an registering means. The rivets can at the same time act as contact means on the printed circuit board, whereby the rivets form an electrical contact between the frame structure and the component to be fixed. Further, the rivet fixing can be applied to fix several different materials. With the aid of the rivet solution according to the invention it is possible to fasten both hard materials, such as metals, and soft materials, such as plastics. Riveting is well suited for extruded materials, because they are readily treated, so that the extrusion material is almost always a suitable material for rivets.
Preferably the fixing means can be integral with the frame structure material, whereby the extruded piece is formed from a single blank. The fixing means can also be a separate part, which is fixed to the structure during the extrusion. Such a piece fixed during the extrusion can be for instance a rivet blank or a threaded pin, which can be used as a fixing means. Also other required components, such as antennas, connectors or carrying strap holders and corresponding components can be fixed during the extrusion.
A separate part fixed during the extrusion can advantageously be used for instance when a certain location requires material characteristics which differ from the rest of the frame structure. The fixed part can differ from the extruded material for instance regarding wear resistance, conductivity or hardness, whereby two materials with different characteristics can be reliably combined when the separate part is fixed to the structure during the extrusion. The fastening of the separate part will also require no extra space, because the part is substantially fastened to the interior of the frame structure wall. The fastening method of the invention provides a strong joint and a fast fixing.
Another possibility to form a fixing means during the extrusion is to make strips or clamping edges at the edge of the frame structure, whereby these strips or edges are bent for instance by rolling or pressing them in some other way over the edge of the component to be fixed. Then a rolled edge clamps the fixed component firmly against the frame""s edge. The fixing means can extend over the whole edge or be shorter than the edge, whereby there may be one or more such means on the same edge. By making the fixing means according to the invention on the opposite edges of the frame a firm fixing is obtained, which at the same time stiffens the whole structure. When a printed circuit board is clamped to the frame by rolling the printed circuit board also acts as a supporting structure for the whole structure. At the same time it is possible to achieve a good electrical contact between the frame and the clamped component.
In different embodiments of the invention the above mentioned fastening methods can be freely combined in the same structure. For instance, the fixing of a component to be fastened can in the central part be made by riveting and the edges can be clamped by rolling. Such a structure forms an extremely rigid, reliable and advantageous fixing solution for fixing a component.
In addition to fixing printed circuit boards the fixing means according to the invention can be used to fix also other components, such as antennas, display and keyboard units, large-sized separate components and hybrid modules. During extrusion the extruded material is forced to glide through a tool, or along the tool, so that it will be formed according to the extrusion profile of the tool. Extrusion methods are divided in two classes: direct extrusion and indirect extrusion. In direct extrusion the product glides in the direction of the pusher. Direct extrusion is used primarily to produce long profile bars. In indirect extrusion the product glides against the pusher direction forming e.g. a body with a bowl shape. For instance aluminum, copper, brass, zinc, lead and also some steel grades are used as raw materials. However, the most common and most used material is aluminum and its alloys. The extrusion can be performed either as hot extrusion or as cold extrusion, where, however, the blanks are heated to a soft state before extrusion in order to increase the shaping characteristics.
The design of different devices can be essentially simplified with the aid of the frame structure according to the invention, because with the aid of the extrusion method it is possible to make a wide diversity of different protecting and fixing means in one manufacturing step. In one manufacturing step it is possible to obtain, not only the desired form of the extruded product, but also the fixing means required to fix the components which shall be fastened to the structure. At the same time it is possible to form a structure divided into compartments, whose partitions make the structure more rigid. At the same time it is possible to make any required registering pins in the casing structure in order to facilitate the assembly. All this is achieved by a suitable tool selection, whereby it is easy to make different forms both rapidly and reliably only by changing tools. The material can be selected according to the application. It is for instance possible to make of aluminum and its alloys different structures which are optimized regarding corrosion durability. Of metals, for instance the above mentioned aluminum or aluminum alloys, it is also possible to make tight structures which act as RF shields.